Two-dimensional optical element array and two-dimensional waveguide apparatus

ABSTRACT

A two-dimensional optical element array with a high alignment precision of optical elements on a substrate and a high long-term reliability is provided. A two-dimensional optical fiber array  10  includes a stacked plurality of optical fiber array units  5  each having an optical fiber  1  and a substrate  2 , the substrate  2  having one or more grooves  21  each suited to a profile of the optical fiber  1  on one of surfaces thereof, and one or more optical fibers  1  being aligned and fixed in grooves  21 , and is characterized in that optical fiber array units  5  are stacked in a state that surfaces facing each other of substrates  2  among adjacent two units out of said plurality array units  5  are not contacted directly, and that said adjacent two units do not give a direct mechanical influence each other.

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT

[0001] The present invention relates to a two-dimensional opticalelement array and a two-dimensional waveguide apparatus. Specifically,this invention relates to a two-dimensional optical element array with ahigh alignment precision of optical elements (optical fiber, lens, forexample) on a substrate and a high long-term reliability, and atwo-dimensional waveguide apparatus having high density and capacity andallowing the number of steps in packaging or connection to be reduced.

[0002] Recently, with the increased communications data capacity, ademand for an optical cross-connect switch technique that provides ahigher throughput of communications data has been increased. Forexample, there has been used an optical switch that is manufacturedusing the MEMS (micro-electro-mechanical-system) for conducting finemachining in a semiconductor process including silicon etching, which isused for micro-machining and the like. Besides, with the increaseddemand for reliability, as well as the demand for the higher throughput,a surface-emitting laser enabling communications with high definitionand stability has come into common use.

[0003] In such an optical switch or surface-emitting laser, an opticalelement array is used (optical fiber array, lens array, waveguide (PLC)array, semiconductor laser (LD) array, photo diode (PD) array, forexample). In the description hereinafter, the “optical fiber array” istaken as an example of the optical element array. In consideration ofrequirements for increased throughput and space-saving, the opticalfiber array is a so-called two-dimensional optical fiber array(occasionally abbreviated as 2DFA hereinafter) whose cross-section takenalong a plane perpendicular to central axes of the aligned opticalfibers has a two-dimensional (hierarchical) configuration.

[0004] For example, as shown in FIG. 16, there has been proposed aconventional two-dimensional optical fiber array 100 with a pitch in athickness direction determined by controlling a thickness of a substrate102 with V-shaped grooves with high precision, arranging optical fibers101 between the substrates 102 with V-shaped grooves and between theuppermost substrate 102 with V-shaped grooves and the fixing member 103,and stacking the substrates in such a manner that a front surface ofeach substrate 102 with V-shaped grooves is brought into contact with aback surface of the adjacent substrate 102 with V-shaped groove (forexample, JP-A56-113114).

[0005] A waveguide substrate (unit) 205 having one or more waveguides201 patterned near a surface thereof, shown in FIG. 17, has been used ina splitter, AWG or waveguide modulator, for example. FIG. 17(a) is aschematic plan view of a splitter with one channel input and eightchannel outputs, and FIG. 17(b) is a cross-sectional view taken along aline X-X in FIG. 17(a).

[0006] However, the conventional two-dimensional optical fiber arrayshave problems as described below.

[0007] (1) It is difficult to control the thickness of a substratehaving V-shaped grooves on a surface thereof (substrate with V-shapedgrooves, simply referred to as a substrate occasionally hereinafter)with a precision of the order of submicrons, and the industrial limit oferror for the entire surface of the substrate is approximately ±1 μm.For example, if eight substrates each having a thickness error of +1 μmare stacked, the resulting 2DFA has a thickness error of +7 μm at themaximum. Thus, the alignment precision of the optical fibers isinevitably low.

[0008] (2) Since the substrates abut on each other, the thickness of anadhesive layer therebetween is substantially 0. This is unfavorable foradhesion for most adhesives. In particular, if the substrates abut oneach other over the substantially entire surface, the long-termreliability thereof is not always sufficiently assured.

[0009] (3) In the case where the upper substrate of adjacent twosubstrates serves as a fixing member for the lower substrate, includingthe case where it serves as a lid, it is inevitably required to adopt amethod of “optical fiber array formation (FA formation) after stacking”,in which the substrates are stacked and ferruled, and then the opticalfibers are inserted, or a method of “FA formation simultaneous withstacking”, in which the optical fibers are placed in the V-shapedgrooves of the lowermost substrate before the second lowest substrate ispositioned and placed on the lowermost substrate, the optical fibers areplaced in the V-shaped grooves of the second lowest substrate before thethird lowest substrate is positioned and placed on the second lowestsubstrate, and such a process is successively carried out. In the caseof the former method of “FA formation after stacking”, in order toassure the precision, a hole, into which the optical fiber is to beinserted, has to be designed to minimize a clearance from the opticalfiber. Thus, the hole is so small that it is extremely difficult toassemble the optical fibers without cutting. For example, in the case ofthe 2DFA comprising stacked eight substrates each having eight opticalfibers aligned thereon, the number of optical fibers to be inserted is64. Also in the case of the latter method of “FA formation simultaneouswith stacking”, the process is complicated and it is difficult toassemble the optical fibers without cutting. In addition, it isextremely difficult to simultaneously conduct positioning of thesubstrate and alignment of optical axes in each substrate includingparallelization.

[0010] (4) In order to solve the above problem (3), there has beenproposed an optical fiber array having, between the substrates withV-shaped grooves stacked one on another, an accommodation section foraccommodating an optical fiber presser member (equivalent to the fixingmember in this invention) in a state where the tops of the opticalfibers protrude slightly from the V-shaped grooves and the optical fiberpresser member on one substrate is kept from contact with the othersubstrate with V-shaped grooves (Japanese Patent No. 3108241). Thisoptical fiber array is superior in that it has enhanced workability andalignment precision because a procedure of stacking after FA formationcan be adopted. However, the above-described problems (1) and (2)associated with the alignment precision and the long-term reliability,respectively, has not been solved yet.

[0011] (5) As another approach for solving the above problem (3), therehas been proposed an optical fiber multicore connector for having agroove for an optical fiber and a rod for aligning axes of connectorterminals (JP-A-55-45051). With the optical fiber multicore connector,although the procedure of FA formation simultaneous with stacking isinvolved, the workability is enhanced because the positioning isaccomplished automatically by the action of the V-shaped grooves and theoptical fibers. And, the above problem (2) of the long-term reliabilitycan be solved depending on the setting of the depth of the groove.However, the above problem (1) of the alignment precision remains, andit is difficult to align the V-shaped grooves on both surfaces of asubstrate with those on another substrate in the width direction. Thus,an additional problem of misalignment in the width direction has arisen.

[0012] (6) An optical communication network involving thetwo-dimensional optical fiber arrays described above has variousconnection points therein. The connection points each reflect lightpassing therethrough, and when the reflected light is launched againinto its original fiber, a laser or the like is disadvantageouslyaffected (a noise occurs, for example). In particular, in the case ofthe 2DFA mainly used for the MEMS switch or the like, since lenscoupling is often adopted, and a space is provided immediately after the2DFA, the reflected light, which is launched into the original fiberagain, has a significant influence.

[0013] (7) To eliminate the disadvantage described above, in the past,reflection from an end face has been suppressed by providing an ARcoating (which is formed by stacking an SiO₂ film and a TiO₂ film eachhaving a thickness of ¼λ and has a total thickness of the order of awavelength of light (λ)) on the substrate and a light-emitting end faceof the optical element, thereby enhancing reflection characteristics atthe end faces. However, the AR coating film is easily degraded byeffects of temperature, humidity and other environmental factors andadversely affects the reflection characteristics. Recently, inparticular, with the development of the wavelength division multiplex(WDM) communication, the quantity of light transmitted through oneoptical fiber has been increased, and accordingly, the possibility of alocal change in characteristics or local degradation due to theincreased quantity of light (light with increased intensity) has beenincreased. Besides, since the AR coating is provided on the end face ofthe fiber array when the fibers are mounted thereon, it is difficult touse a vacuum processing for vapor deposition of the AR coating. Thus,multiple AR coatings cannot be conducted at a time, and the cost isincreased.

[0014] In addition, the above-described waveguide substrate has aproblem as follows. When connecting the waveguide substrates and theoptical fiber arrays with each other, each of the optical fiber arraysneeds to be optically aligned with one of the waveguide substrates. Inthis alignment, the waveguide substrate and the optical fiber array arealigned with each other on the level of submicrons, and thus, thealignment inevitably requires extremely high precision and many processsteps.

[0015] The present invention has been devised in view of theabove-describe problems, and an object of this invention is to provide atwo-dimensional optical element array with a high alignment precision ofoptical elements (optical fiber, lens, for example) on a substrate and ahigh long-term reliability, and a two-dimensional waveguide apparatushaving high density and capacity and allowing the number of steps inpackaging or connection to be reduced.

SUMMARY OF THE INVENTION

[0016] After the earnest research, the inventor has found that the aboveproblems can be solved by stacking a plurality of optical element arrayunits, each of which is a set of a substrate and one or more opticalelements aligned and fixed in the grooves thereof, in such a manner thatsurfaces of the substrates of adjacent optical element array units,which face to each other, are kept from direct contact with each otherand from having a direct mechanical influence on each other (the sameapplies to a plurality of waveguide substrate units each having one ormore waveguides patterned thereon in a planar manner). Thus, thisinvention has been completed.

[0017] Specifically, this invention is to provide a two-dimensionaloptical element array and a two-dimensional waveguide substrateapparatus as described below.

[0018] Firstly, there is provided a two-dimensional optical elementarray, comprising: a stack of a plurality of optical element array unitseach having an optical element and a substrate, the substrate having oneor more grooves each suited to a profile of the optical element on oneof surfaces thereof, and one or more optical elements being aligned andfixed in the grooves, characterized in that said plurality of opticalelement array units are stacked in a state that surfaces facing eachother of the substrates among adjacent two units out of said pluralityof optical element array units are not contacted directly each other,and that said adjacent two units do not give a direct mechanicalinfluence each other Here, “the state that said adjacent two units donot give a direct mechanical influence each other” means “the state thata force, vibration or the like is not directly transmitted among theadjacent two units each other”, and the same applies to the followingdescription.

[0019] It is preferable that the optical element in said two-dimensionaloptical element array is an optical fiber or lens.

[0020] It is preferable that an apex of an optical element arranged on asubstrate of a first optical element array unit is brought into contactwith a surface of a substrate of a second optical element array unitboth of which face each other, but that the surfaces of the substratesof adjacent two optical element array units are not contacted directlyeach other, and that said adjacent two units do not give a directmechanical influence each other in said two-dimensional optical elementarray.

[0021] It is preferred to stack the plurality of optical element arrayunits in such a manner that an adhesive layer is interposed between anapex of an optical element arranged on the substrate of a first opticalelement array units and a surface of a substrate of a second opticalelement array unit both of which face each other, that the apex of anoptical element arranged on a substrate of a first optical element arrayunit is brought into contact with a surface of a substrate of a secondoptical element array unit both substrates of first and second unitsface each other, but that the surfaces of the substrates of adjacent twooptical element array units are not contacted directly each other, andthat said adjacent two units do not give a direct mechanical influenceeach other in said two-dimensional optical element array.

[0022] According to the present invention, there is also provided with atwo-dimensional optical element array, which further comprises a fixingmember on one of surf aces of the substrate of the uppermost opticalelement array unit and between the substrates of adjacent opticalelement array units, the fixing member pressing or mounting the opticalelement against or on one surface with the grooves of the substrate foralignment and fixing.

[0023] It is further provided with a two-dimensional optical elementarray in which the fixing member presses or mounts the optical elementagainst or onto the surface with the grooves of the substrate foralignment and fixing in such a manner that a surface of the fixingmember and a surface of the substrate of the optical element array unitwhich faces to the surface of the fixing member are not contacteddirectly each other, and that said adjacent two units do not give adirect mechanical influence each other.

[0024] It is further provided with a two-dimensional optical elementarray of which optical element is pressed against or mounted on saidsubstrate for alignment and fixing in such a manner that said opticalelement abuts on a surface of said fixing member and on a side wall ofsaid groove(s).

[0025] It is also preferable that said optical element array unit(s)further comprise(s) an adhesive layer disposed between the surface ofsaid fixing member and the surface of said substrate of said opticalelement array unit which faces to the surface of the fixing member.

[0026] It is also preferable that a thickness of said adhesive layerfalls within a range from 2 to 100 μm.

[0027] It is also preferable to form a positioning guide at apredetermined position on the surface with said grooves of saidsubstrate of said optical element array unit.

[0028] It is also preferable that said groove is a V-shaped groove.

[0029] It is preferable to slant a light-emitting end face and/or lightreceiving end face of the optical element of the optical element arrayunit by a predetermined angle (θ) with respect to a plane perpendicularto a central axis of the optical element.

[0030] It is also preferable to dispose the light-emitting end faceand/or light receiving end face of the optical element in the planeperpendicular to the central axis of the optical element.

[0031] It is also preferable to dispose the light-emitting end faceand/or light receiving end face of the optical element in a plane angledby a predetermined angle (θ) with respect to the plane perpendicular tothe central axis of the optical element.

[0032] It is also preferable to dispose the light-emitting end faceand/or light receiving end face of the optical element in a planeperpendicular to an optical axis of an emitted light and/or incidentlight, respectively.

[0033] According to the present invention, it is further provided with amethod of measuring a core position of an optical element of thetwo-dimensional optical element array which comprises the steps of

[0034] measuring core positions of m rows of optical elements andmeasuring core positions of at least two of n columns of opticalelements, in the case where m optical element array units are stackedand each optical element array unit has n channels (in the case wherethe optical elements are arranged in m rows and n columns);

[0035] designating arbitrarily one optical element for each of the atleast two columns of optical elements and measuring a distance D betweenthe core positions of the optical elements designated (designatedoptical elements); and

[0036] calculating a positional relation among elements of a matrix ofthe core positions of the optical elements at four corners of arectangular having a line segment connecting the core positions of thedesignated optical elements as a diagonal line thereof and calculatingthe core positions of all of the optical elements.

[0037] According to the present invention, there is provided with atwo-dimensional waveguide apparatus, comprising a stack of a pluralityof waveguide substrate units each having one or more waveguidespatterned in a planar manner,

[0038] characterized in that the plurality of waveguide substrate unitsare stacked in a state that the surfaces of the substrates of adjacenttwo optical element array units are not contacted directly each other,and that said adjacent two units do not give a direct mechanicalinfluence each other.

[0039] There is further provided with a two-dimensional waveguideapparatus which further comprises an adhesive layer between the surfacesfacing each other of two adjacent waveguide substrate units of theplurality of waveguide substrate units.

[0040] It is preferable that a thickness of said adhesive layer fallswithin a range from 2 to 100 μm.

[0041] It is also preferable to form a positioning guide at apredetermined location on a surface of the waveguide substrate unit.

[0042] It is also preferable to slant a light-emitting end face of eachwaveguide of the waveguide substrate unit by a predetermined angle (θ)with respect to a plane perpendicular to an optical axis thereof.

[0043] There is further provided with a two-dimensional waveguideapparatus, in which the light-emitting end face and/or light receivingend face of the waveguide of the waveguide substrate unit is disposed ina plane perpendicular to a central axis of the waveguide.

[0044] There is also provided with a two-dimensional waveguide apparatusin which the light-emitting end face and/or light receiving end face ofthe waveguide of the waveguide substrate unit is disposed in a planeangled by a predetermined angle (θ) with respect to the planeperpendicular to the central axis of the waveguide.

[0045] There is also provided with a two-dimensional waveguide apparatusin which the light-emitting end face and/or light receiving end face ofthe waveguide of the waveguide substrate unit is disposed in a planeperpendicular to an optical axis of an emitted light and/or incidentlight, respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

[0046]FIG. 1 is a schematic cross-sectional view of a two-dimensionaloptical fiber array, which is a first embodiment of a two-dimensionaloptical element array according to this invention.

[0047]FIG. 2 is an enlarged cross-sectional view of a part of a groovein a substrate in FIG. 1.

[0048]FIG. 3 is a schematic cross-sectional view of a two-dimensionaloptical fiber array, which is a second embodiment of the two-dimensionaloptical element array according to this invention.

[0049] FIGS. 4(a) and (b) are a schematic cross-sectional view of atwo-dimensional optical fiber array, respectively, which is a thirdembodiment of the two-dimensional optical element array according tothis invention. FIG. 4(b) is an enlarged schematic cross-sectional viewof the portion A in a two-dimensional optical fiber array shown in FIG.4(a).

[0050]FIG. 5 is a schematic cross-sectional view of a two-dimensionaloptical fiber array, which is a fourth embodiment of the two-dimensionaloptical element array according to this invention.

[0051]FIG. 6 is a schematic cross-sectional view of a two-dimensionaloptical fiber array, which is a fifth embodiment of the two-dimensionaloptical element array according to this invention.

[0052]FIG. 7 is a cross-sectional view illustrating a relationshipbetween reflection characteristics and an angle deviation (<θ) of thetwo-dimensional optical fiber array of the fourth embodiment shown inFIG. 5.

[0053]FIG. 8 is a cross-sectional view illustrating a relationshipbetween reflection characteristics and an angle deviation (<θ) of thetwo-dimensional optical fiber array of the fifth embodiment shown inFIG. 6.

[0054]FIG. 9 is a schematic cross-sectional view of a two-dimensionaloptical fiber array, which is a sixth embodiment of the two-dimensionaloptical element array according to this invention.

[0055]FIG. 10 schematically illustrates an arrangement of a simplein-line switch.

[0056]FIG. 11 is a cross-sectional view for schematically illustrating aguide pin jig used for provide a two-dimensional configuration of thetwo-dimensional optical fiber array, which is an embodiment of thetwo-dimensional optical element array of this invention.

[0057] FIGS. 12(a) and 12(b) are plan view and cross-sectional view,respectively, schematically showing one embodiment of a two-dimensionalwaveguide apparatus of this invention.

[0058] FIGS. 13(a) and 13(b) are cross-sectional views taken along aline Z-Z in FIG. 12(a) and showing two aspects of this invention.

[0059]FIG. 14 is a schematic plan view for illustrating a method ofstacking waveguide substrate units to provide a two-dimensionalconfiguration in one embodiment of the two-dimensional waveguideapparatus of this invention.

[0060] FIGS. 15(a) and 15(b) are plan view and side view, respectively,schematically showing a state where the two-dimensional optical fiberarray and a one-dimensional optical fiber array are connected to eachother via the two-dimensional waveguide apparatus.

[0061]FIG. 16 is a schematic cross-sectional view of an exemplaryconventional two-dimensional optical element array (optical fiberarray).

[0062] FIGS. 17(a) and (b) are a schematic cross-sectional view of anexemplary conventional waveguide apparatus, and FIG. 17(a) is aschematic plan view, and FIG. 17(a) is a cross-sectional view takenalong a line X-X in FIG. 17(a).

[0063]FIG. 18 is a schematic cross-sectional view of one of theembodiments wherein an optical fiber is housed in a through hole formedin a cylindrical member in the two-dimensional optical element arrayaccording to the present invention.

[0064]FIG. 19 is a schematic cross-sectional view of one of theembodiments wherein an optical fiber for maintaining polarized wave isused as an optical fiber in the two-dimensional optical element arrayaccording to the present invention.

[0065] FIGS. 20(a) and (b) are a schematic cross-sectional view ofanother embodiment wherein an optical fiber is housed in a through holeformed in a cylindrical member in the two-dimensional optical elementarray according to the present invention; FIG. 20(a) being across-sectional view vertical to the axis of the optical fiber, and FIG.20(b) being a cross-sectional view taken along a line X-X in FIG. 20(a).

[0066]FIG. 21 is a schematic cross-sectional view of still anotherembodiment wherein an optical fiber is housed in a through hole formedin a cylindrical member in the two-dimensional optical element arrayaccording to the present invention.

[0067]FIG. 22 is a schematic cross-sectional view of still anotherembodiment wherein an optical fiber is housed in a through hole formedin a cylindrical member in the two-dimensional optical element arrayaccording to the present invention.

[0068]FIG. 23 is a schematic cross-sectional view of still anotherembodiment wherein an optical fiber is housed in a through hole formedin a cylindrical member in the two-dimensional optical element arrayaccording to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0069] Now, referring to the drawings, embodiments of a two-dimensionaloptical element array and a method of manufacturing the same of thisinvention will be described specifically with respect to a case where anoptical element is constituted by an optical fiber, for example.

[0070]FIG. 1 is a schematic cross-sectional view of a two-dimensionaloptical fiber array, which is a first embodiment of the two-dimensionaloptical element array according to this invention. As shown in FIG. 1, atwo-dimensional optical fiber array 10 in this embodiment comprises astack of a plurality of optical fiber array units 5 each having anoptical fiber 1 and a substrate 2, the substrate 2 has one or moregrooves 21 each suited to a profile of the optical fiber 1 on one ofsurfaces thereof, and one or more optical fibers 1 are aligned and fixedin the grooves 21. The optical fiber array units 5 are stacked in such amanner that surfaces facing each other of the substrates 2 of twoadjacent optical fiber array units 5 are are not contacted directly eachother, and that said adjacent two units do not give a direct mechanicalinfluence each other (in FIG. 1, for example, in such a state that anupper surface (with the grooves 21) 22 of a substrate 2 a of thelowermost optical fiber array unit 5 a and a lower surface (backsurface) 23 of a substrate 2 b of the second lowest optical fiber arrayunit 5 b are not contacted directly each other, and that said adjacenttwo units do not give a direct mechanical influence each other.

[0071] With such an arrangement, the alignment precision of the opticalfibers on the substrate does not depend on a thickness precision of thesubstrate, and therefore, can be enhanced. Unlike a conventional stackof the optical fiber array units 5 having the substrates 2 brought intocontact with each other, the stacking precision does not depend on thethickness precision of the substrate 2. Since the need to control thethickness precision of the substrate 2, which is extremely difficult, iseliminated, the alignment precision of the optical fibers on thesubstrate can be readily increased without intricacy.

[0072] In this embodiment, in addition to the fact that the alignmentprecision of the optical fibers does not depend on the thicknessprecision of the substrate, the alignment precision of the opticalfibers on the substrate can be readily enhanced by positioning theoptical fiber with a positioning jig or stacking the optical fiber arrayunits 5 with cores thereof being aligned, as described later.

[0073] As shown in FIG. 1, the optical fiber array 10 of this embodimentpreferably further comprises fixing members 3 on one of surfaces of asubstrate 2 d of the uppermost optical fiber array unit 5 d and betweenthe substrates 2 (2 a, 2 b, for example) of adjacent optical fiber arrayunits 5 (5 a, 5 b, for example), in which the fixing member presses ormounts the optical fiber 1 against or on one surface with the grooves 21of the substrate 2 (2 d, 2 a and 2 b, for example) for fixing andalignment.

[0074] In this case, the materials of the substrate 2 and the fixingmember 3 are not limited particularly. However, as a preferred example,the materials may be borosilicate glass, which is transparent.

[0075] With such an arrangement, the state where surfaces facing eachother of the substrates 2 of two adjacent optical fiber array units 5are not contacted directly each other, and that said adjacent two unitsdo not give a direct mechanical influence each other can be readilyprovided.

[0076] In the two-dimensional optical fiber array 10 in this embodiment,as shown in FIG. 1, the fixing member 3 preferably aligns and fixes theoptical fibers 1 onto the surface with the grooves 21 of the substrate 2in such a manner that a surface of the fixing member 3 and a surface ofthe substrate of the optical fiber array unit 5 which faces to thatsurface of the fixing member 3 are not contacted directly each other,and that said adjacent two units do not give a direct mechanicalinfluence each other (in FIG. 1, for example, in such a manner that thetwo surfaces of a fixing member 3 a disposed on the lowermost opticalfiber array unit 5 a and surfaces 22, 23 of the substrates 2 a, 2 b ofthe optical fiber array units 5 a, 5 b, which face to that two surfacesof the fixing member 3 a, respectively, are not contacted directly eachother, and that said adjacent two units do not give a direct mechanicalinfluence each other. In this case, as described later, a lower surface(back surface) of the fixing member 3 a abuts on an upper part of theoptical fiber 1 on the substrate 2 a and thus is kept from contact withthe surface 22, so that the two surfaces have no influence on eachother. And, an upper surface (front surface) of the fixing member 3 aabuts on an adhesive layer 4, described later, and thus is kept fromdirect contact with the surface 23, so that the two surfaces have noinfluence on each other.

[0077] With such an arrangement, it can be readily provided that thealignment precision of the optical fibers does not depend on thethickness precision of the substrate.

[0078] Furthermore, as shown in FIGS. 1 and 2, in the two-dimensionaloptical fiber array 10 of this embodiment, the optical fiber 1 ispreferably pressed against or mounted on the substrate 2 for alignmentand fixing in such a manner that the optical fiber 1 abuts on side walls21 a, 21 b of the groove 21 and on a surface 3 s of the fixing member 3.In this way, the optical fiber abuts on the surface 3 s of the fixingmember 3 with the upper part thereof protruding above the surface of thesubstrate 2, and on the side walls 21 a, 21 b of the groove 21.

[0079] With such an arrangement, it can be readily provided that thealignment precision of the optical fibers is not influenced, dependingon the thickness precision of the substrate.

[0080] As shown in FIG. 1, the two-dimensional optical fiber array 10 ofthis embodiment preferably further comprises an adhesive layer 4 betweenthe surface of the fixing member 3 and the surface other than that withthe grooves (back surface) of the substrate 2 of the optical fiber arrayunit 5 which faces to that surface of the fixing member 3 (for example,between the upper surface (front surface) of the fixing member 3 a andthe surface other than that with the grooves (back surface) of thesubstrate 2 b of the optical fiber array unit 5 b).

[0081] The adhesive layer 4 used in this embodiment is not limited to aparticular one. However, in the case where the substrate 2 and thefixing member 3 are made of transparent borosilicate glass or the like,it may preferably be an ultraviolet curing adhesive, for example.

[0082] While the thickness of the adhesive layer 4 depends on the typeof the adhesive used, it preferably falls within a range from 2 to 100μm, and more preferably within a range from 3 to 20 μm. If it is below 2μm, an insufficient adhesivity may be resulted, or the optical fiberarray units may be partly brought into contact with each other if thesubstrate precision is low, thereby degrading the precision. If it isbeyond 100 μm, an influence of thermal expansion or curing shrinkage maybecome negligible.

[0083] With such an arrangement, since the adhesive layer having anappropriate thickness lies between the FAs, the adhesivity of theadhesive can be elicited adequately, and thus, a good long-termreliability can be assured.

[0084] In the case of Japanese Patent No. 3108241, which discloses anoptical fiber array having an accommodation section for accommodating anoptical fiber presser member (equivalent to the fixing member in thisinvention), an adhesive layer can partially assured between the opticalfiber array units, such as at a part between the optical fiber pressermember of one substrate with V-shaped grooves and another substrate withV-shaped grooves. However, in the substrate with a complicatedthree-dimensional configuration, various and complicated stresses aregenerated due to curing shrinkage of the adhesive, shrinkage or tensiondue to thermal fluctuation after curing, or the like, and crackingthereof may possibly be caused. In addition, peeling thereof may occurat a periphery of the abutting surface, thereby reducing the long-termreliability. On the contrary, the adhesion mechanism of thetwo-dimensional optical fiber array of this embodiment is a simpleadhesion mechanism of two flat plates. Accordingly, such complicatedstresses do not occur and a high long-term reliability is attained.

[0085] Incidentally, the present two-dimensional includes a one in whichat least one cylindrical member 302 having a through hole 302 a capableof housing an optical fiber being passed therethrough is provided. Inthis case, a substrate in which at least one groove 302 a correspondingto the outer form of the one cylindrical member 302 is formed on atleast one surface thereof may be used as a substrate 303. For example, acylindrical member 302 having a through hole 302 a is tentatively fixedto a groove 303 a formed on a substrate 303 to give a ferrule. Then, anoptical fiber 301 a is inserted into a through hole 302 a of thecylindrical member 302 in the ferrule. Finally, a two-dimensionaloptical element array 310 in which a plural number of cylindricalmembers 302 having a through hole 302 a through which an optical fiberhas been housed by passing it therethrough is stacked two-dimensionallyon a plural number of the substrates layered may be manufactured byfixing substrates 303, cylindrical members 302 and fixing members 304finally by means of adhering with an adhesive or the like.

[0086] Since an optical fiber is usually made of a quartz, an opticalfiber shows such a property that it is reliable to break when a stressis concentratedly given to a damage formed on its surface if the quartzreceives a damage on its surface. In the case of a two-dimensionaloptical element array 310 having such a constitution as shown in FIG.18, the reliability as a two-dimensional optical element array may beimproved since the breakage of the fiber caused by the damage formed dueto the contact of the outer surface of the core with the substrates 303and the like may be effectively protected. This is because the opticalfiber 301 a is aligned and fixed in a state that the fiber is housed inthe cylindrical member 302. Furthermore, the work for aligning andfixing optical fibers 301 a is simple and it can be shortened since itdoes not require a complicated operation such as taking and turning thefibers. This may improve not only the productivity, but also thereliability since the chance of the breakage caused by contacting fiberswith substrates 303 and the like may be reduced. This is because theworking time may be shortened as mentioned above. In case of the fiberfor maintaining polarized wave 301 c, this method is preferred in thepoint that the capacity maintaining polarized wave is not deterioratedsince the unnecessary stress does not occur because the stress beingderived from the adhesive layers 305 and given to the fiber formaintaining polarized wave 301 c is almost even. This is because thethickness of the adhesive layer around the fiber for maintainingpolarized wave 301 c becomes almost even since the fiber for maintainingpolarized wave 301 c is inserted into the through hole 302 a of thecylindrical member 302, as shown in FIG. 19. In this respect, note thatthe numeral figure 306 denotes a stress giving member and the numeralfigure 307 denotes a core, respectively.

[0087] In case of said two-dimensional optical element array providedwith a cylindrical member, as shown in FIG. 20, it is preferred that thethrough hole 302 a of the cylindrical member 302 has a reverse taperedportion 302 b which widens towards the opening of the hole from whichthe bared optical fiber obtained by pealing the outer cover 301 b isinserted in the point that the insertion of the optical fiber 301 a intothe through hole of the cylindrical member may be achieved smoothly.Additionally, it is preferred that the side end portion 302 c of theopening of the reverse tapered portion 302 b extrudes outwardly at alength of 1 μm or more from the end of the substrate 303 b and the endof the fixing member 304 a, when the surface roughness of both thecorresponding substrate 303 b and the corresponding fixing member 304 ais taken into consideration in the point that the breakage of the fibercaused by the contact with the substrate 303 b and the fixing member 304a may be effectively protected. Moreover, the extrusion of the side endportion is preferably 5 mm or less.

[0088] Any material may be used for a cylindrical member 302 without anyspecial limitation, as far as such a material may be subjected to aneasy precise processing, and can protect sufficiently an optical fiber301 a to be housed in the through hole 302 a from being damaged due tothe contact with the outer environments. In the case that the fixationwith the substrate 303 is carried out by using an ultraviolet curingadhesive, it is preferable to use a transparent material. For example, aborosilicate glass may be preferably used.

[0089] An outer diameter of the cylindrical member 302 may be chosen,depending upon the size of an optical fiber 301 a and the like. Thus, itis difficult to determine easily an optimum size of the outer diameterthereof. However, one may use preferably a cylindrical member havingusually an outer diameter of 0.25 to 2.7 mm. The inner diameter of thethrough hole 302 a is preferable set at a size larger than the outerdiameter of the optical fiber 301 a. It is preferable to set it at thediameter of from 0.126 to 0.13 mm.

[0090] Said grooves being provided with (a) cylindrical member(s)according to the present two-dimensional optical fiber element arrayinclude, as shown already in FIG. 18, at least one groove 303 a whichcorresponds to the outer shape of the cylindrical member. There is nolimitation in the shape of the groove formed in the substrate as far asit has shape corresponding to the outer shape of the cylindrical member,aligns the cylindrical member smoothly to hold it surely. For example, aV-shaped groove capable of fixing surely the cylindrical member at threepoints may be preferably used. As to the space for disposing the grooves303 a, one may dispose the grooves, as shown in FIG. 20(a), by aligningthem so as to have a predetermined space between the cylindricalmembers. One may dispose them by aligning so as to make the cylindricalmembers contact intimately, as shown in FIG. 21, either.

[0091] Said substrate being provided with (a) cylindrical member(s)according to the present two-dimensional optical fiber element array mayhave, on the both surfaces, for example as shown already in FIG. 22,grooves 303 a being capable of aligning cylindrical members 302 andcorresponding to the outer shape of the cylindrical member 302; saidgrooves 302 a being disposed in almost the same shape each other andalmost at an equal distance. One may manufacture a two-dimensionaloptical fiber element array 310 wherein two sheets of the substrates aredisposed layered by facing the grooves 303 a each other, a cylindricalmember 302 is sandwiched and aligned between said two substrates 303,and another cylindrical member 302 is aligned and fixed on the uppersurface of the upper substrate 303, by using this type of the substrate.

[0092] In case of a substrate having grooves on the both surfaces asshown in FIG. 22, one may make the positioning of the cylindricalmember(s) 302 on the substrate 303 precisely and easily by processingthe grooves 302 a quite precisely on the both surfaces thereof almost inthe same shape and the same disposing distance. Accordingly, one maymanufacture a two-dimensional optical fiber element array 310 having thecylindrical members 303 on the both surfaces positioned in a higherpreciseness each other, compared with the substrate 303 shown in FIG.18. This is because one may set more precisely the distances of from thecenter to the center among the upper and lower cylindrical members 303being disposed two-dimensionally and layered in the relationship withthe cylindrical members 303 facing each other or adjacent each other.Furthermore, one may also set more precisely the distances of from thecenter to the center among the upper, middle and lower cylindricalmembers 303 being disposed three-layered in the relationship with thecylindrical members 303 facing each other or adjacent each other bydisposing and aligning the cylindrical member 303 on the lower surfaceof the lower substrate, as shown in FIG. 23.

[0093]FIG. 3 is a schematic cross-sectional view of a two-dimensionaloptical fiber element array, which is a second embodiment of thetwo-dimensional optical element array according to this invention. Asshown in FIG. 3, the two-dimensional optical fiber array 10 preferablyfurther comprises a positioning guide 6 formed at a predeterminedposition in the surface with the grooves 21 of the substrate 2 of theoptical fiber array unit 5. The positioning guide 6 shown in FIG. 3 isformed on the surface having the grooves 21 formed therein of thesubstrate 2, and thus can be efficiently machined simultaneously withthe grooves 21.

[0094] With such an arrangement, the optical fiber array units 5 can bereadily positioned with an appropriate positioning jig (not shown) orstacked with the cores thereof aligned, and thus, the alignmentprecision of the optical fibers on the substrate can be enhanced.

[0095] The groove used in the embodiments described above can have anyconfiguration so far as it is suited to the profile of the optical fiber1 and can align the optical fibers 1 smoothly and fix them withreliability. However, it is preferably a V-shaped groove capable ofsupporting the optical fiber 1 at three points.

[0096] In the manufacture of the two-dimensional optical fiber array ofthe above described embodiment, an optical fiber array unit isfabricated first, which is a set of a substrate and one or more opticalfibers aligned and fixed in the grooves thereof. This is a usual processof aligning and fixing the optical fibers on one surface of thesubstrate, and thus the risk of cutting the optical fiber, for example,is low. Also when stacking, the optical fibers are stacked in the formof the optical fiber array unit, and therefore the risk of cutting theoptical fiber is low. Furthermore, the stacking is carried outindependently, so that the positioning is relatively readily carriedout. Currently, some two-dimensional optical fiber arrays (2DFA) areneeded to have about 1000 cores (for example 32×32). As the number ofthe cores is increased, the advantage of being capable of assemblywithout cutting becomes more remarkable.

[0097]FIG. 4 is a schematic cross-sectional view of a two-dimensionaloptical fiber array (with no fixing member 3 (see FIG. 1)), which is athird embodiment of the two-dimensional optical element array accordingto this invention. As shown in FIG. 4, the two-dimensional optical fiberarray 10 may comprise a plurality of optical fiber array units 5 stackedin such a manner that an adhesive layer 4 (4 a, 4 b) is interposedbetween an apex of an optical fiber 1 arranged on a substrate 2 of anoptical fiber array unit 5 (5 a, 5 b) and a surface of another substrate2 (2 a, 2 b) of an optical fiber array unit 5 opposing thereto, the apexof the optical fiber 1 and the surface of the substrate 2 (2 a, 2 b) arebrought into contact with the adhesive layer 4 (4 a, 4 b), and thesurfaces facing each other of the substrates 2 (2 a, 2 b) of adjacentoptical fiber array units 5 (5 a, 5 b) are not contacted directly eachother, and that said adjacent two units do not give a direct mechanicalinfluence each other. Here, the adhesive layer 4 a connects and fixesthe optical fiber array units 5 with each other, and the adhesive layer4 b connects and fixes the substrate 2 and the optical fiber 1 with eachother. The adhesive layer may be omitted, as far as there can berealized the state where the surfaces facing each other of adjacentsubstrates 2 (2 a, 2 b) are not contacted directly each other, and thatsaid adjacent two units do not give a direct mechanical influence eachother.

[0098]FIGS. 5 and 6 are schematic cross-sectional views oftwo-dimensional optical fiber arrays, which are fourth and fifthembodiments of the two-dimensional optical element array according tothis invention, respectively. As shown in FIGS. 5 and 6, in thetwo-dimensional optical fiber array 10 in these embodiments, the opticalfiber 1 of the optical fiber array unit 5 has a light-emitting end faceS slanted by a predetermined angle (θ) with respect to a plane Vperpendicular to a central axis L of the optical fiber. While only thelight-emitting end face S is slanted in FIGS. 5 and 6, a light-receivingend face may be slanted, or both of the light-emitting end face S andthe light-receiving end face may be slanted.

[0099] With such an arrangement, the reflection characteristics of theend face of the optical element (optical fiber) on the substrate forreceiving or emitting light can be enhanced and maintained for a longperiod, and a loss of quantity of light and an adverse effect to anotherdevice can be prevented. That is, the light is reflected toward theoutside of the optical fiber core, so that it is not launched into theoriginal fiber, and thus, good reflection characteristics can beattained. In addition, since, in order to enhance the reflectioncharacteristics, the optical fiber is directly machined to have aslanting on light-emitting end face, any peeling or degradation, whichwould be found in the AR coating film, does not occur. For an intenselight, it is only a matter of durability of the optical fiber, and theslanting itself is not a disadvantage. Besides, the slanting end facecan be formed by simply polishing the end face in a slanting direction,and therefore, is superior in cost.

[0100] In this case, the light-emitting end faces S and/orlight-receiving end faces of the optical fibers 1 may be disposed in theplane V perpendicular to the central axes of the optical fibers 1, asshown in FIG. 5. Alternatively, as shown in FIG. 6, the light-emittingend faces S and/or light-receiving end faces of the optical fibers 1 maybe disposed in a plane U angled at a predetermined angle (θ) withrespect to the plane V perpendicular to the central axes of the opticalfibers 1. While the end faces are slanted by a predetermined angle in acolumn direction (thickness direction) in FIGS. 5 and 6, the end facesmay be slanted in a row direction (width direction).

[0101] As described above, the 2DFA often involves lens coupling, forwhich a close investigation of the optical system is required. Forexample, in the case where light is launched into a lens in a slantingdirection, an allowable limit of an angle deviation (<θ) (which is adeviation of an optical axis of a planar microlens from the optical axisof the light emitted from the optical fiber (light launched into theplanar microlens)) is on the order of 15 degrees, although depending oncharacteristics of the lens (if the light is launched into the lens at aright angle, <θ=0°). If the angle deviation (<θ) is larger than 15degrees, the coupling has to be accomplished with a closer tolerance,and a loss occurs in practical. Therefore, from the viewpoint ofoperability of the optical system, the angle deviation (<θ) ispreferably 10 degrees or less.

[0102] As shown in FIG. 7, in the fourth embodiment shown in FIG. 5, ifthe slant angle θ of the end faces S of the optical fibers 1 is set at 8degrees, and a common quartz SM fiber (with a refractive index of 1.45)and a planar microlens 7 are used for spatial lens coupling, an equalfocal length can be attained for the optical fibers 1 without slantingthe planar microlens 7, because the end faces S of the optical fibers 1are arranged in the plane V perpendicular to the central axes L thereof.In this case, if conditions are the same as conventional, the angledeviation (<θ) is small, specifically 3.6 degrees, which facilitatescoupling with high efficiency.

[0103] Here, the angle deviation (<θ) can be calculated from thefollowing equation (1).

[0104] (Equation 1)

<θ=−sin⁻¹(1.45×sinθ)+θ  (1)

[0105] If the angle θ is set at 8 degrees, the angle deviation (<θ) ofthe optical axis Q of the planar microlens from the optical axis P ofthe light emitted from the optical fiber 1 is 3.6 degrees from theequation (1).

[0106] As shown in FIG. 8, in the fifth embodiment shown in FIG. 6, ifthe angle θ is similarly set at 8 degrees, and a common quartz SM fiber(with a refractive index of 1.45) is used for spatial lens coupling, theangle deviation (<θ) of the optical axis Q of the planar microlens fromthe optical axis P of the light emitted from the optical fiber 1,calculated from the equation (1), is 11.6 degrees. In this case, toprovide an equal focal length for the optical fibers, the planarmicrolens 7 shown is slanted to be parallel to the end faces S of theoptical fibers, that is, by 8 degrees.

[0107] To prevent a light from being reflected back to (launched againinto) the end face S of the optical fiber in the 2DFA, if a commonquartz fiber is used, only needed is to provide the slant angle of theend face equal to or more than 8 degrees. Besides, to provide the angledeviation (<θ) equal to or less than 15 degrees, if the common quartzfiber is used, only needed is to provide the slant angle θ of the endface of the optical fiber equal to or less than 28 degrees in the fourthembodiment shown in FIG. 5, or to provide the slant angle of the endface of the optical fiber equal to or less than 15 degrees in the fifthembodiment shown in FIG. 6. Furthermore, to provide the angle deviation(<θ) equal to or less than 10 degrees, only needed is to provide theslant angle θ equal to or less than 20 degrees in the fourth embodimentshown in FIG. 5.

[0108]FIG. 9 is a schematic cross-sectional view of a two-dimensionaloptical fiber array, which is a sixth embodiment of the two-dimensionaloptical element array according to this invention. As shown in FIG. 9,in a two-dimensional optical fiber array 10 in the sixth embodiment, thelight-emitting end faces S and/or light-receiving end faces of theoptical fibers 1 are arranged in a plane W perpendicular to the opticalaxis P of the incident or emitted light. Here, FIG. 9 shows a case wherethe light-emitting end faces S are arranged in the plane W perpendicularto the optical axis P of the emitted light.

[0109] With such an arrangement, the light is launched into the planarmicrolens 7, for example, at a right angle. Therefore, the opticalsystem can be simplified, thereby enhancing the operability thereof, andvariations in optical length can be eliminated.

[0110] In any embodiment described above, a lens array in the planarmicrolens 7 typically has a regular pitch. If the orientations andangles of the angled layers are different from each other, the lightbeams are not launched into or emitted from the respective layers lightwith a regular pitch, and thus, the orientations and angles of therespective angled layers are preferably the same.

[0111] A recent cross-connect switch has been required to realizeextremely quick switching. If there are variations in switching opticalpath length, variations in switching time disadvantageously result.Thus, it is important to provide an equal switching optical path length.While a conventional arrangement results in variations in the switchingoptical path length, this embodiment can provide an equal switchingoptical path length. It can be said that this embodiment is particularlyadvantageous in an application where an equal optical path length isrequired as in the case shown in FIG. 5.

[0112] In FIG. 10, there is schematically shown an arrangement of asimple in-line switch. Here, since the switching element depends on thearrangement and method adopted, the optical path length in the elementis not taken into consideration. In the arrangement shown in FIG. 10, anoptical path length from an input-side fiber array 24 to an in-lineoptical switch 26 is denoted by L1, and optical path lengths from thein-line optical switch 26 to an output-side fiber array 25 are denotedby L2 and L3. Then, a total optical path length is L1+L2 in the case ofswitching (1), or L1+L3 in the case of switching (2). In the arrangementshown in FIGS. 10(a) and 10(b), the lengths L2 and L3 are not the same,and therefore, the total optical path length varies depending onswitching ((1) or (2)). On the contrary, in the arrangement shown inFIG. 10(c), the lengths L2 and L3 are the same, and therefore, the totaloptical path length does not vary depending on switching. Thus, it canbe said that this arrangement is more advantageous in an applicationwhere an equal optical path length is required.

[0113] For example, the MEMS switch has typically a large inter-elementpitch of the order of 3 mm to reduce a loss and crosstalk. Assuming thatthe 2DFA has 10 columns and 10 rows and the slant angle of the end faceof the optical fiber is 8 degrees, a pitch from a first layer to a tenthlayer is 27 (3×9) mm, and thus, the optical path length difference |L−1|is 3.8 (27×tan8) mm, which cannot be neglected. Since the optical pathlength difference depends on the slant angle of the optical fiber endface, the optical fiber pitch or the like, it cannot be uniquelydetermined. However, it can be said that this embodiment is preferred inthe case where the optical path length difference |L−1| is equal to ormore than 1 mm.

[0114] Now, referring to FIGS. 1 to 3, a method of manufacturing atwo-dimensional optical element array (optical fiber array) of thisinvention will be described.

[0115] For example, a method of manufacturing a two-dimensional opticalfiber array 10 of this invention comprises a step of forming an opticalfiber array unit 5 by aligning and fixing one or more optical fibers 1on a substrate 2 having, on one surface thereof, one or more grooves 21each suited to a profile of the optical fiber 1, and a step of stackinga plurality of optical fiber array units 5, and is characterized in thatthe optical fiber array units 5 are stacked in a state that surfacesfacing each other of the substrates 2 of two adjacent optical fiberarray units 5 are not contacted directly each other, and that saidadjacent two units do not give a direct mechanical influence each other(in FIG. 1, for example, in a state that an upper surface (with thegrooves 21) 22 of a substrate 2 a of the lowermost optical fiber arrayunit 5 a and a lower surface (back surface) 23 of a substrate 2 b of thesecond lowest optical fiber array unit 5 b are not contacted directlyeach other, and that said adjacent two units do not give a directmechanical influence each other (the same thing applies to othersubstrates)).

[0116] Thus, in the manufacture of the two-dimensional optical fiberarray, as described above, an optical fiber array unit is fabricatedfirst, which is a set of a substrate and one or more optical fibersaligned and fixed in the grooves thereof. This is a usual process ofaligning and fixing the optical fibers on one surface of the substrate,and thus the risk of cutting the optical fiber, for example, is low.Also when stacking, the optical fibers are stacked in the form of theoptical fiber array unit, and therefore the risk of cutting the opticalfiber is low. Furthermore, the stacking is carried out independently, sothat the positioning is relatively readily carried out. Currently, sometwo-dimensional optical fiber arrays (2DFA) are needed to have about1000 cores (for example 32×32). As the number of the cores is increased,the advantage of being capable of assembly without cutting becomes moreremarkable.

[0117] In this case, preferably, during or after aligning and fixing theone or more optical fibers 1 to form the optical fiber array unit 5, aplurality of fixing members 3 for pressing or mounting the optical fiber1 against or on one surface with the grooves 21 of the substrate 2 (2 d,2 a and 2 b, for example) for fixing and alignment are disposed on oneof surfaces of a substrate 2 d of the uppermost optical fiber array unit5 d and between the substrates 2 (2 a, 2 b, for example) of adjacentoptical fiber array units 5 (5 a, 5 b, for example), and then, aplurality of optical fiber unit arrays 5 with the fixing members 3 arestacked.

[0118] The fixing members 3 are preferably disposed on one surface ofthe substrate 2 and between the substrates 2 in such a manner that asurface of the fixing member 3 and a surface of the substrate 2 of theoptical fiber array unit 5 which faces to that surface of the fixingmember 3 are not contacted directly each other, and that said adjacenttwo units do not give a direct mechanical influence each other (in FIG.1, for example, in such a manner that the two surfaces of a fixingmember 3 a disposed on the lowermost optical fiber array unit 5 a andsurfaces 22, 23 of the substrates 2 a, 2 b of the optical fiber arrayunits 5 a, 5 b, which face to that two surfaces of the fixing member 3a, respectively, are not contacted directly each other, and that saidadjacent two units do not give a direct mechanical influence eachother).

[0119] The optical fiber 1 is preferably pressed against or mounted onthe substrate 2 for alignment and fixing in such a manner that theoptical fiber 1 abuts on a surface of the fixing member 3 and side walls21 a, 21 b of the groove 21.

[0120] When stacking a plurality of optical fiber array units 5 with thefixing members 3, an adhesive layer 4 is preferably provided between thesurface of the fixing member 3 and the surface other than that with thegrooves (back surface) of the substrate 2 of the optical fiber arrayunit 5 which face to that surface of the fixing member 3 (for example,between the upper surface (front surface) of the fixing member 3 a andthe surface other than that with the grooves (back surface) of thesubstrate 2 b of the optical fiber array unit 5 b).

[0121] The thickness of the adhesive layer 4 preferably falls within arange from 2 to 100 μm.

[0122] The substrate 2 of the optical fiber array unit 5 having apositioning guide 6 formed at a predetermined position in the surfacewith the grooves 21 is preferably used.

[0123] The groove 21 is preferably a V-shaped groove.

[0124] When manufacturing the optical fiber array 10 with no fixingmember 3 (see FIG. 1) as shown in FIG. 4, a plurality of optical fiberarray units may be stacked in such a manner that the apexes of theoptical fibers arranged on the substrate of one optical fiber array unitis brought into contact with a surface of the substrate of the opticalfiber array unit opposing thereto, thereby the surfaces facing eachother of the substrates of two adjacent optical fiber array units arenot contacted directly each other, and said adjacent two units do notgive a direct mechanical influence. Alternatively, a plurality ofoptical fiber array units may be stacked in such a manner that anadhesive layer is interposed between the apexes of the optical fibersarranged on the substrate of one optical fiber array unit and a surfaceof the substrate of the optical fiber array unit opposing thereto, andthe apexes of the optical fibers and the surface of the substrate arebrought into contact with the adhesive layer, thereby the surfacesfacing each other of the substrates of adjacent optical fiber arrayunits are not contacted directly each other, and said adjacent two unitsdo not give a direct mechanical influence each other.

[0125] In this case, a temporary fixing member (not shown) can be usedto make the optical fiber abut against the V-shaped groove in the stepof fabricating each optical fiber array unit, and after the assembly ofthe optical fiber array unit, the temporary fixing member can be removedto stack the optical fiber array units. In this case, removal of thetemporary fixing member can be facilitated if the fixing member is madeof fluororesin, such as tetrafluoroethylene, or a mold release agent isapplied on the substrate.

[0126] With such an arrangement with no fixing member, the totalthickness of the optical fiber array can be readily reduced. In general,the pitch in the thickness direction (stacking direction) depends on thethickness of each optical fiber array unit and cannot be less than that.To make the pitch narrower, each optical fiber array unit has to be madethinner. However, there is a limit in terms of strength. In the casewhere each optical fiber array unit comprises the substrate and thefixing member, a limit thickness thereof is a sum of a limit thicknessof the substrate and a limit thickness of the fixing member. If thefixing member is omitted, however, the limit thickness of each opticalfiber array unit is equal to the limit thickness of the substrate, andaccordingly, the pitch in the thickness direction (stacking direction)can be reduced. Specifically, the limit thickness of the substrate is onthe order of 0.5 mm, and the limit thickness of the fixing member is onthe order of 0.4 mm. Thus, the limit thickness of the optical fiberarray unit, which would be about 0.9 mm if it comprises the substrateand the fixing member, can be reduced to about 0.5 mm by omitting thefixing member.

[0127] Another advantage of the fact that the fixing member is omitted(each optical fiber array unit comprises the substrate and the opticalfibers) is that an adverse effect due to a high coefficient of thermalexpansion (α) of the adhesive layer can be avoided. If the fixing memberis used, it is also needed to bond the substrate and the fixing memberwith the adhesive layer. Experimentally, the adhesive layer preferablyhas a thickness of the order of 30 μm, and the adhesive layer betweenthe optical fiber array units has a thickness of the order of 10 μm. Thetotal thickness of the adhesive layer for one layer is on the order of40 μm, and thus, the effect of the coefficient of thermal expansion (α)of the adhesive layer cannot be neglected. Specifically, if thecoefficient of thermal expansion (α) of the adhesive layer used in thisembodiment is on the order of 10×10⁻⁶, borosilicate glass (manufacturedby Corning Incorporated, trade name: Pyrex) is used for the substrate,and the pitch is 1.5 mm (a case of Example 1 described later), the wholetwo-dimensional optical fiber array including the adhesive layersbetween the substrates and the fixing members has different coefficientsof thermal expansion (α) in the width direction and in the thicknessdirection, specifically, 33×10⁻⁷ in the width direction and 58×10⁻⁷ inthe thickness direction. Since the MEMS optical switch or the like isformed on a surface of silicon (Si) or the like, it essentially shouldnot have a direction dependency of thermal expansion, and thus, theabove-described direction dependency of thermal expansion may become aproblem.

[0128] To solve this problem, the adhesive layer can be reduced inthickness. If the fixing member is omitted, the thickness of theadhesive layer can be reduced without any other special measures. Thethickness of the adhesive layer between the optical fiber array units isabout 10 μm. One reason for this is that, according to a commonmanufacturing method, the substrate and the fixing member each have avariation in thickness on the order of ±3 μm, and therefore, a variationin thickness thereof on the order of ±6 μm needs to be taken intoaccount for each optical fiber array unit. In other words, the thicknessof the adhesive layer between the optical fiber array units on the orderof 10 μm implies that the thickness of the adhesive layer approximatelyfalls within a range of 10±6 μm, and is, at the minimum, about 4 μm. Ifthe fixing member is omitted, only the variation in thickness of thesubstrate on the order of 3 μm needs to be taken into account. Thus, inorder to assure the minimum thickness of 4 μm, it is sufficient that thethickness of the adhesive layer approximately falls within a range of7±3 μm, and in other words, the adhesive layer has a thickness on theorder of 7 μm. That is, the thickness of the adhesive layer per layer inthis case is on the order of 7 μm. In this case, the coefficient ofthermal expansion (α) in the thickness direction is 37×10⁻⁷, and thedirection dependency of thermal expansion can be neglected.

[0129] As shown in FIGS. 5 and 6, when manufacturing the two-dimensionaloptical fiber array of this invention, the light-emitting end face Sand/or light-receiving end face of the optical fiber 1 of the opticalfiber array unit 5 may be slanted by a predetermined angle (θ) withrespect to the plane V perpendicular to the central axis L of theoptical fiber 1. In this case, the light-emitting end faces S and/orlight-receiving end faces of the optical fibers 1 may be disposed in theplane V perpendicular to the central axes L of the optical fibers, asshown in FIG. 7. Alternatively, as shown in FIG. 8, the light-emittingend faces S and/or light-receiving end faces of the optical fibers 1 maybe disposed in the plane U angled at a predetermined angle (θ) withrespect to the plane V perpendicular to the central axes L of theoptical fibers. Furthermore, as shown in FIG. 9, the light-emitting endfaces S and/or light-receiving end faces of the optical fibers 1 may bedisposed in the plane W perpendicular to the optical axes P of theemitted light and/or the incident light.

[0130] With such an arrangement, it is possible to manufacture,efficiently and at low cost, the two-dimensional optical element arraywhich has superior reflection characteristics of the light-emitting orlight-receiving end face of the optical element on the substrate, andcan maintain the superior reflection characteristics for a long periodand prevent a loss of quantity of light and an adverse effect to anotherdevice.

[0131] For example, the light-emitting or light-receiving end face S ofthe optical fiber may be slanted as follows: optical fibers areincorporated with each optical fiber array unit and fixed thereto withan adhesive; the end faces S are polished with a lap polisher or thelike, as in the case of a typical one-dimensional optical fiber array,in such a manner that the end faces S are inclined by a desired anglewith respect to the surface plate of the lap polisher; and thus, the endfaces can have a slant of the desired angle.

[0132] A two-dimensional optical fiber array formation (2DFA formation)after the two-dimensional optical fiber array unit is fabricated in themethod of manufacturing a two-dimensional optical fiber array of thisinvention will be described in detail below.

[0133] A first method of two-dimensional optical fiber array formationmay be to stack and fix the optical fiber array units while activelyadjusting them. For example, the optical fiber array units may bestacked and fixed with an adhesive or the like while launching whitelight into the light-emitting or light-receiving end faces of thetwo-dimensional optical fiber array units at the side opposite to thelight-receiving or light-emitting end faces thereof, observing lightemitted from the optical fibers with a CCD camera to know the positionsof the optical fibers, and adjusting relative positions between theoptical fiber array units. If a plurality of optical fiber array unitsare stacked and fixed simultaneously, a large-scale apparatus needs tobe used therefor. Therefore, the stacking and fixing thereof arepreferably carried out one after another.

[0134] A device for securely holding the optical fiber array unit ispreferably used to prevent a displacement from the determined positionthereof due to curing shrinkage when the adhesive is cured.

[0135] For example, a method involving a guide pin jig, as shown in FIG.11, is suitable. As shown in FIG. 11, first, the lowermost optical fiberarray unit 5 a is disposed between first guide pins 6 a and second guidepins 6 b, one each of which is provided on each of two vertical beamjigs of a guide pin jig 11. Then, in order to assure contact between theguide pins and guide grooves of the V-shaped grooved substrate of theFA, a load G1 is exerted on the lowest optical fiber array unit 5 a bypulling the same downwardly. Next, the second lowest optical fiber arrayunit 5 b is disposed between the second guide pins 6 b and third guidepins 6 c, and in order to assure contact between the guide pins and theguide grooves of the V-shaped grooved substrate of the FA, a load G2 isexerted on the optical fiber array unit 5 b by pressing the same fromabove. In this state, an ultraviolet curing adhesive is spread betweenthe optical fiber array units 5 a and 5 b, and irradiated withultraviolet rays for curing. Here, since any adhesive flowing into theguide groove causes the guide pin to be fixed thereto, the adhesive iscarefully made to flow only between the V-shaped grooved substrate ofthe optical fiber array unit 5 a and the upper lid substrate of theoptical fiber array unit 5 b. For third lowest and upper optical fiberarray units 5, as in the case of the optical fiber array units 5 b, theoptical fiber array unit 5 is disposed between the guide pins, the loadG2 is exerted thereon from above, and the optical fiber array unit isfixed with the adhesive. The same process is conducted up to the eighthlayer to provide a stack.

[0136] Assuming that an optical axis is the z-axis, an axis extending inthe stacking direction is the y-axis, and an axis perpendicular to thez-axis and the y-axis and extending in the direction of arranging theoptical fibers on one substrate is the x-axis, alignment of the opticalfiber array units in the directions of the x- and y-axes is preferablyconducted while observing beam centers through image recognition, and anoptical axis parallelism θy for each layer is preferably adjusted byobserving a distance in the direction of the z-axis through anauto-focus function or a scheme for searching a beam waist. Besides, anoptical axis parallelism θx is preferably adjusted so that the bottomsurfaces of the substrates with V-shaped grooves of the optical fiberarray units stacked one on another are parallel to each other and spacedapart from each other by a desired distance by observing the opticalfiber array units from a side. Since the bottom surface of the substratewith V-shaped grooves and the line formed by the V-shaped grooves areparallel to each other, both the θx and the θz can be adjusted accordingto this method. With this method, although a device used becomescomplicated, the two-dimensional optical fiber array formation (2DFAformation) can be conducted with reliability.

[0137] A second two-dimensional optical fiber array formation may be toposition the optical fiber units by using a guide groove (positioningguide) 6 provided on the optical fiber array unit 5 and a positioningguide pin adapted to the guide, as shown in FIG. 3. In this case, alarge-scale positioning device is not needed, and only a high-precisionguide pin jig is needed. Since both the V-shaped grooves 21 for theoptical fibers and the V-shaped guide grooves 6 can be provided on oneand the same surface of the substrate 2 with V-shaped grooves, quitehigh precision of the V-shaped grooves 21 for the optical fibers and theV-shaped guide grooves 6 can be assured in terms of the positions, aswell as the parallelism thereof. That is, according to this method, thepositions in x and y directions and the optical axis parallelisms θx,θy, and θz can be adjusted simultaneously, and quite high workability isprovided. Here, the guide groove used for positioning may be used as areference for polishing after stacking, or used for coupling thetwo-dimensional optical fiber array (2DFA) with another optical device.For example, when a user of another existing optical device is to couplea 2DFA with the existing optical device, he/she can use the guide grooveof the 2DFA as a reference parallel to the optical axis. The guidegroove can be omitted for downsizing, if it is not necessary.

[0138] Now, referring to FIG. 1, one embodiment of a method of measuringa core position of an optical element of a two-dimensional opticalelement array of this invention will be described. According to thisembodiment, the method of measuring the core position of the opticalfiber 1 of the above-described two-dimensional optical fiber array 10comprises: a step of measuring core positions of m (four) rows ofoptical fibers 1 and measuring core positions of at least two of n(eight) columns of optical fibers 1, in the case where m (four inFIG. 1) optical fiber array units 5 are stacked and each optical fiberarray unit has n (eight in FIG. 1) channels (in the case where theoptical fibers 1 are arranged in m (four) rows and n (eight) columns); astep of arbitrarily designating one optical fiber 1 for each of the atleast two columns of optical fibers 1 and measuring a distance D betweenthe core positions of the designated optical fibers 1 (shown asdesignated optical fibers 1 a in FIG. 1); and a step of calculating apositional relation among elements of a matrix of the core positions ofthe optical fibers 1 at four corners of a rectangular having the linesegment connecting the core positions of the designated optical fibersla as a diagonal line thereof and calculating the core positions of allof the optical fibers 1.

[0139] Specifically, in FIG. 1, in which the optical fiber array units 5are referred to as rows 1 to 4 from the bottom, and the columns ofoptical fibers are assigned reference characters A to H from left toright, the core positions of the rows 1 to 4 each having eight columns(eight channels) are measured, and the core positions of the columns Aand H each having four rows (four channels) are measured. In addition,assuming that the optical fibers 1 associated with the matrix elements(1,A) and (4,H) are the designated optical fibers 1 a, a diagonaldistance D between the two points is measured. Based on the triangle(1,A) (4,H) (1,H) consisting of three sides of the diagonal line(1,A)-(4,H), the line (1,A)-(1,H) of the row 5 a and the line(1,H)-(4,H) of the column H, a positional relation between the row 5 aand the element (4,H) in the row 5 d can be determined. Similarly, bymeasuring the length of the diagonal line (4,A)-(1,H) and the length ofthe line (1,A)-(4,A) of the column A, a positional relation between therow 5 a and the element (4,A) in the row 5 d can be determined based onthe triangle (1,A) (4,A) (1,H). The positional relations between the row5 a and the row 5 d and between the row 5 a and the columns A and H thusdetermined can be combined with the positional data for the respectiverows to provide a matrix of core positions. In this case, the corepositions may be calculated by measuring the length of the diagonal linebetween the optical fibers designated based on the core positions of allcolumns and arbitrary two rows.

[0140] Furthermore, the columns to be measured are not limited to thecolumns A and H described above. However, since a larger distancebetween the columns would reduce influence of individual errors on thewhole measurement, the columns at both ends are preferably measured.Besides, the designated optical fibers 1 a are not limited to the matrixelements (1,A) and (4,H). However, since a large distance between thedesignated optical fibers 1 a would reduce influence of individualerrors on the whole measurement, the outermost optical fibers arepreferably selected.

[0141] An apparatus used for implementation of the method of measuring acore position of an optical element of a two-dimensional optical elementarray of this invention is not limited particularly, as far as thecoordinate of the core position of the optical element of thetwo-dimensional optical element array can be measured and calculatedwithin the measurement system through an image processing, lengthmeasuring or the like, and there is no need to use any dedicatedmeasurement apparatus.

[0142]FIG. 12 schematically illustrates one embodiment of atwo-dimensional waveguide apparatus of this invention, in which FIG.12(a) is a plan view and FIG. 12(b) is a cross-sectional view takenalong a line Y-Y in FIG. 12(a). As shown in FIG. 12, a two-dimensionalwaveguide apparatus 200 of this embodiment comprises a stack of aplurality of waveguide substrate units 205 each having one or morewaveguides 201 patterned in a planar manner, in which the plurality ofwaveguide substrate units 205 are stacked in such a manner that surfacesfacing each other of two adjacent waveguide substrate units 205 of theplurality of waveguide substrate units 205 are not contacted directlyeach other, and that said adjacent two units do not give a directmechanical influence each other.

[0143] With such an arrangement, the density and capacity thereof can beenhanced and the number of steps in packaging or connection can bereduced.

[0144] In this case, an adhesive layer 204 is preferably providedbetween the surfaces facing each ohter of two adjacent waveguidesubstrate units 205 of the plurality of waveguide substrate units 205.As the adhesive layer 204, the same as in the above-describedtwo-dimensional optical fiber array can be used.

[0145] The thickness of the adhesive layer 204 preferably falls within arange from 2 to 100 μm as in the case of the above-describedtwo-dimensional optical fiber array.

[0146]FIG. 13(a) is a cross-sectional view taken along a line Z-Z inFIG. 12(a) illustrating one aspect of this invention, and FIG. 13(b) isa cross-sectional view taken along the line Z-Z in FIG. 12(a)illustrating another aspect of this invention. As shown in FIG. 13, andas in the case of the two-dimensional optical fiber array describedabove, in the two-dimensional waveguide apparatus 200 of thisembodiment, a light-emitting end face S′ and/or light-receiving end faceof the waveguide 201 of the waveguide substrate unit 205 is slanted by apredetermined angle (θ) with respect to a plane V′ perpendicular to acentral axis L′ of the waveguide.

[0147] In this case, the light-emitting end faces S′ and/orlight-receiving end faces of the waveguides 201 of the waveguidesubstrate units 205 may be disposed in the plane V′ perpendicular to thecentral axes L′ of the waveguides, or may be disposed in a plane U′angled at a predetermined angle (θ) with respect to the plane V′perpendicular to the central axes L′ of the waveguides. Alternatively,as in the case of the two-dimensional optical fiber array shown in FIG.9, the light-emitting end faces S′ and/or light-receiving end faces ofthe waveguides of the waveguide substrate units may be disposed in aplane perpendicular to the optical axis of the emitted light and/orincident light.

[0148] As one example of a method of manufacturing a two-dimensionalwaveguide apparatus of this invention, there is a method ofmanufacturing a two-dimensional waveguide apparatus by stacking aplurality of waveguide substrate units 205 each having one or morewaveguides 201 patterned in a planar manner, in which the plurality ofwaveguide substrate units 205 are stacked in such a manner that surfacesfacing each other of two adjacent waveguide substrate units 205 of theplurality of waveguide substrate units 205 are not contacted directlyeach other, and that said adjacent two units do not give a directmechanical influence each other (see FIG. 12).

[0149] In this case, an adhesive layer 204 may be provided between thesurfaces facing each other of two adjacent waveguide substrate units 205of the plurality of waveguide substrate units 205.

[0150] The thickness of the adhesive layer 204 preferably falls within arange from 2 to 100 μm.

[0151] Each of the light-receiving or light-emitting end faces S′ of thewaveguides 201 of the waveguide substrate units 205 may be slanted by apredetermined angle (θ) with respect to the plane V′ perpendicular tothe central axes L′ of the waveguides (see FIG. 13).

[0152] In this case, the light-emitting end faces S′ and/orlight-receiving end faces of the waveguides 201 of the waveguidesubstrate units 205 may be disposed in the plane V′ perpendicular to thecentral axes L′ of the waveguides, or the light-emitting end faces S′and/or light-receiving end faces of the waveguides 201 of the waveguidesubstrate units 205 may be disposed in a plane U′ angled at apredetermined angle (θ) with respect to the plane V′ perpendicular tothe central axes L′ of the waveguides. Alternatively, as in the case ofthe two-dimensional optical fiber array shown in FIG. 9, thelight-emitting end faces and/or light-receiving end faces of thewaveguides of the waveguide substrate units may be disposed in a planeperpendicular to the optical axis of the emitted light and/or incidentlight.

[0153] As a method of stacking the waveguide substrate units 205 to forma two-dimensional waveguide apparatus, the same method as in theabove-described two-dimensional optical fiber array can be used. In thiscase, for example, a positioning guide formed at a predeterminedlocation on a surface of the waveguide substrate unit may be involved.FIG. 14 shows a case where four chips of waveguides 201 are formed on asingle wafer with center lines thereof aligned, and positioning guides206 are formed on both sides of the waveguides 201. These waveguides 201can be formed by photolithography, for example. From the single waferthus processed, the waveguide substrates to be stacked are cut andreserved. Thus, even if positions of the positioning guides 206 intransverse and depth directions with respect to the waveguides 201 arenot absolutely precise, precision of stacking can be assured because thewaveguide substrates to be stacked have the positioning guides alignedwith each other.

[0154]FIG. 15 schematically illustrates a state where a two-dimensionaloptical fiber array and a one-dimensional optical fiber connected toeach other via a two-dimensional waveguide apparatus, in which FIG.15(a) is a plan view, and FIG. 15(b) is a side view. In FIGS. 15, aone-dimensional optical fiber array 110 with four channels, turned 90degrees, is connected to a two-dimensional optical fiber array 10 witheight channels via the two-dimensional waveguide apparatus 200. Thetwo-dimensional waveguide apparatus 200 comprises four waveguidesubstrate units 201 and a fixing member 3 stacked one on another, andthe two-dimensional optical fiber array 10 comprises four optical fiberarray units 5 and a fixing member 3 stacked one on another.

[0155] As described above, when connecting the waveguide substrates andthe optical fiber arrays with each other, each of the optical fibersneeds to be optically aligned with one of the waveguide substrates. Inthis alignment, the waveguide substrate and the optical fiber array arealigned with each other on the level of submicrons, and thus, there hasbeen a problem in that the alignment inevitably requires extremely highprecision and many process steps. However, with such an arrangement, onealignment process allows four substrates to be aligned, and thus, thenumber of steps in alignment and connection can be reducedsubstantially.

[0156] This invention will be described in more detail below withreference to an example. However, this invention should not be limitedby the example in any sense.

EXAMPLE 1

[0157] A two-dimensional optical fiber array (2DFA) with 8-by 8-corehaving pitches of 1.5 mm in lateral and thickness directions wasfabricated. An optical fiber array unit had a width of 13 mm and athickness of 1.49 mm (total thickness of a substrate with V-shapedgrooves and a fixing member), and an adhesive layer between opticalfiber array units had a thickness of 10 μm. To attain high reliability,it is preferable that the adhesive layer has a thickness of about 10 to20 μm. However, since the adhesive layer has a high thermal coefficientof thermal expansion, the value 10 μm was adopted to prevent thecoefficient of thermal expansion of the whole device from being so high.

[0158] An epoxy resin adhesive, which has low curing ratio (2%) was usedto fabricate the optical fiber array unit, and stack and fix the opticalfiber array units. In the phase of stacking, the optical fiber arrayunit is held by a guide pin jig until the resin is cured in order toprevent the array from being displaced due to curing shrinkage. However,since a large curing shrinkage results in a large stress remaining inthe form of a remaining distortion, the epoxy resin adhesive having lowcuring shrinkage was used.

[0159] As a method of stacking and fixing, the above-describedtwo-dimensional optical fiber array formation was adopted, and the guidegroove pitch was 15 mm. The optical fiber array units was not subject toend face polishing separately, but subject to polishing collectivelyafter stacking. For the polishing, as shown in FIG. 3, the substratewith V-shaped grooves was made to outwardly protrude in the widthdirection from the fixing member, and a side of the substrate withV-shaped grooves was used as a reference plane for polishing. The sideof the substrate with V-shaped grooves can be readily cut to be parallelto the V-shaped grooves in the phase of processing the substrate.Protruding the reference plane outwardly is preferred in the case wherenot only the polishing reference but also a relationship for the opticalaxis need to be known. For example, in the case where theabove-described first two-dimensional optical fiber array formation isadopted, by protruding the reference plane outwardly, holding the sidesof the substrates with V-shaped grooves can always assure a certainconstant precision of the optical axis parallelism θy, and thus, theadjustment of θy becomes easy.

[0160] In measurement of core positions of the two-dimensional opticalfiber array after stacked, a device that can measure core positions onlyfor one dimension at a time was used. Therefore, positions of cores ineach layer were measured one layer after another, positions of firstcores in the respective layers and positions of eighth cores in therespective layers were measured in the thickness direction, measurementwas conducted for one diagonal line, and then the measurement resultswere combined to provide accurate core positions.

[0161] In the core position measurement, a satisfactory result wasobtained: an error of an optical fiber having a maximum displacementfrom an ideal matrix coordinate (one of the 64 optical fibers of achannel having a maximum displacement) was not more than 2 μm. In thisexample, since the guide groove was not necessary, the sides were cut toreduce the width to 13 mm.

[0162] In addition, a thermo cycle test (−40 to 85° C.×70 cycles) and ahigh temperature and high humid test (85° C./85%×2 weeks) were performedon the resulting two-dimensional optical fiber array. As a result, asatisfactory result was obtained without peeling of the adhesive layerbetween the optical fiber array units and the like, or a failure such ascutting of a fiber.

EXAMPLE 2

[0163] The two-dimensional optical fiber array having a low return lossand 8- by 10-channels with a pitch of 1.5 mm and comprising a stack ofoptical fiber array units including optical fibers whose light-emittingend faces are polished to be slanted by a predetermined angle (θ=8°)with respect to the plane perpendicular to the optical axes thereof wasfabricated. In this example, fabrication of the optical fiber arrayunits, stacking of the optical fiber array units, and evaluation of thefabricated two-dimensional optical fiber array were conducted in thisorder.

[0164] Fabrication of Optical Fiber Array Unit

[0165] A substrate of borosilicate glass (coefficient of thermalexpansion: 32×10⁻⁷) was machined to provide a wafer of a size of 50mm×55 mm×1.495 mm (thickness). The wafer was ground to form the V-shapedgrooves for aligning and fixing the optical fibers and the positioningguides (V-shaped guide grooves) thereon. Eight V-shaped grooves wereformed with a pitch of 1.5 mm, and the positioning guides (V-shapedguide grooves) were formed by being shifted 2 mm outward from the firstand eighth V-shaped grooves.

[0166] Then, the wafer was cut into substrate chips of a predeterminedsize, each used for the optical fiber array unit. Since thetwo-dimensional optical fiber array to be provided has 8- by10-channels, 10 substrate chips (optical fiber array units) werefabricated.

[0167] Then, the optical fiber array units were assembled. In thisassembly, the optical fibers were first placed in the V-shaped grooveson the substrate, the optical fibers were pressed against the V-shapedgrooves with a temporary fixing member (the temporary fixing memberitself is not bonded, since it is made of an SUS material 1 mm thick andcoated with fluororesin, such as polytetrafluoroethylene), and anadhesive for fixing (epoxy resin) was spread thereon and irradiated withultraviolet rays for fixing. After the adhesive for fixing was cured,the temporary fixing member was peeled off the substrate to provide theoptical fiber array unit.

[0168] Then, to prevent a coated part of an optical fiber from beingmade free to cause cutting of the optical fiber, an adhesive for fixingthe coating (urethane acrylate resin) was applied to the rear end of theoptical fiber array unit to fix the coated parts of the optical fibers.

[0169] Then, the end face of the optical fiber array unit was polishedto be slanted. In order to make the end face of the optical fiber arrayunit be angled by θ=8°, a dedicated jig was prepared. In this case,assuming that the optical axis extends in the direction of an angle 0°,the slant angle of the end face of the optical fiber array unit is 82°.Using the dedicated angled jig, the end face of the optical fiber arrayunit was coarse-lapped, fine-lapped, and then polished. This resulted inan error of ±0.3° for the angle of 82°.

[0170] Stacking of Optical Fiber Array Units

[0171] There are various methods of stacking the optical fiber arrayunits, and a guide pin jig was used in this example. Here, the “guidepin jig” refers to a jig having guide pins mounted thereon with highprecision for positioning the optical fiber array units in the stackingdirection thereof. The guide pins and the jig substrate was made ofzirconia. A beam, on which the guide pins are to be mounted, hadV-shaped grooves with a pitch of 1.5 mm. The guide pins (diameter: 0.7mm) were inserted into the V-shaped grooves and pressed against with afixing member, thereby setting up the guide pins. In addition, two beamshaving the guide pins need to be positioned relative to each other withhigh precision. Thus, in order to positioning the two beams relative toeach other with high precision, the relative position of the beams withthe pins was precisely defined using a transverse beam and a diagonalbeam.

[0172] The optical fiber array units were disposed between the guidepins mounted on the guide-pin jig sequentially. Here, the guide pins andthe positioning guides (V-shaped guide grooves) formed on the opticalfiber array unit need to be in close contact with each other. Thus, aload was exerted on the optical fiber array unit to assure the contactwith the guide pins. In this case, the load exerted on the optical fiberarray unit was about 30 g. The optical fiber array units need to bealigned in the direction of the optical axes thereof with highprecision. In this example, the optical fiber array unit was abuttedagainst the substrate of the guide pin jig at the end faces thereof,thereby aligning the optical fiber array units. The alignment variationof the end faces of the optical fiber array units was about 10 μm. Inthis way, one optical fiber array units was fixed to the guide pin jig,and a next optical fiber array unit was fixed to the guide pin jig inthe same manner.

[0173] Then, the optical fiber array units were fixed to each other byspreading an adhesive (ultraviolet curing epoxy resin) into a spacetherebetween. The adhesive layer formed between the optical fiber arrayunits was about 10 μm thick. This process was repeated to fabricate thetwo-dimensional optical fiber array comprising ten layers.

[0174] Evaluation of Two-Dimensional Optical Fiber Array

[0175] First, evaluation of the precision of the two-dimensional opticalfiber array fabricated in this example was conducted. The optical fiberarray units were referred to as rows 1 to 10 from the bottom, and thecolumns of optical fibers were assigned reference characters A to H fromleft to right. The core positions of the rows 1 to 10 each having eightchannels were measured, and the core positions of the columns A and Heach having ten channels were measured. In addition, the optical fiberlocated at the matrix element (1,A) and the optical fiber located at thematrix element (10,H) were designated as the designated optical fibers,and a distance between the core positions thereof was measured. All thecore positions of the two-dimensional optical fiber array weredetermined based on the relative position of the lowermost optical fiberarray unit corresponding to the row 1 and the uppermost optical fiberarray unit corresponding to the row 10 thus determined and the corepositions for the columns A and H. A deviation of the core positionmatrix from an ideal core position matrix was calculated.

[0176] As a result, it was confirmed that, for all channels, corepositions of the two-dimensional optical fiber array fabricated in thisexample lie within a range of ±2 μm from their respective positions inthe ideal core position matrix.

[0177] Then, a return loss at the end face of the two-dimensionaloptical fiber array fabricated in this example was evaluated. The returnloss was measured with an optical coherence domain reflectometry (OCDR).Here, the length of the optical fiber from a connector to the array endface of the two-dimensional optical fiber array was about 1.8 m.

[0178] As a result, the return loss at the end face of thetwo-dimensional optical fiber array fabricated in this example wasconfirmed to be 60 dB or more for all channels.

[0179] Then, reliability evaluation of the two-dimensional optical fiberarray fabricated in this example was conducted. The two-dimensionaloptical fiber array was subjected to a thermo cycle test (−40 to 85°C.×70 cycles) and a high temperature and high humid test (85° C./85%×2weeks).

[0180] As a result, it was confirmed that the two-dimensional opticalfiber array fabricated in this example had the same core positionprecision and return loss before and after the tests. Good results wereobtained. That is, the variation in core positions thereof wassufficiently low, specifically 0.3 μm or less, and the return loss wasnot changed.

EXAMPLE 3

[0181] The two-dimensional waveguide apparatus comprising a stack offour splitters each having 1- by 8-channels was connected to thetwo-dimensional optical fiber array. A waveguide core having waveguideswith a pitch of 250 μm (on the side of 8 channels) was placed on a Siwafer having a thickness of 1 mm so as to be 1.03 mm high from thebottom of the Si wafer, and a clad having a thickness of 0.025 mm wasformed thereon, thereby providing a splitter unit having a totalthickness of 1.055 mm. As shown in FIG. 14, four chips of splitters wereformed on one wafer, and positioning guides (grooves) were formed bygrinding on the wafer with a pitch of 5 mm. In order to assure thestacking precision, the wafer was processed in the following manner sothat the center positions, relative depth with respect to the waveguideand pitch of the stacking guide pins placed in the guide grooves areconstant. The wafer was applied to a processing jig, as shown in FIG. 3in Japanese Patent Laid-Open No. 5-273442, so as to be parallel to areference surface for an object to be processed (both of a side surfaceand a bottom surface), and the positioning guides were formed so as tobe parallel to a reference surface of a processing machine, therebyrealizing the accurate relative position thereof. In this case, therequired relationship between the reference surface for an object to beprocessed and the reference surface of the processing machine, such asparallel or orthogonal relationship, was assured. The wafer was cut intosplitter chips, and the splitter chips were stacked and fixed with acore pitch of 1.06 mm in the stacking direction in a stacking mannershown in FIG. 13(b). That is, the adhesive layer between the splitterunits was 5 μm. The end faces of the two-dimensional splitters werepolished to have a shape angled by 8° as shown in FIG. 13(b). Then, thetwo-dimensional optical fiber array having 8- by 4-cores configured asshown in FIG. 1 was fabricated in the same manner as in Example 1. Theend face was polished to be angled by 8° after stacking. The thicknessof the optical fiber array unit (distance from the bottom of theV-shaped grooved substrate to the top of the fiber) was 1.055 mm, thesame as the splitter unit, and the stacking pitch was 1.06 mm. In otherwords, the thickness of the adhesive layer between the optical fiberarray units was 5 μm. In addition, a signle-layer (one-dimensional)optical fiber array having four cores with a pitch of 1.06 mm wasfabricated. The end face thereof was polished to be angled 8° so as tobe parallel to the end face of the two-dimensional splitter when it isconnected thereto (that is, in a direction of arrangement of opticalfibers of the one-dimensional optical fiber array). These three werealigned with each other, connected to each other, and fixed to eachother as in the case of a typical waveguide splitter module to provide atwo-dimensional splitter module.

[0182] Although the two-dimensional splitter module fabricated in thisexample had a connection loss of 0.5 dB and a return loss of 60 dB,which are a little larger than those for a one-dimensional splittermodule, the two-dimensional splitter module had characteristics suitablefor practical use.

[0183] As described above, this invention can provide a two-dimensionaloptical element array with a high alignment precision of opticalelements (optical fiber, lens, for example) on a substrate and a highlong-term reliability, and a two-dimensional waveguide apparatus havinghigh density and capacity and allowing the number of steps in packagingor connection to be reduced.

What is claimed is:
 1. A two-dimensional optical element array,comprising: a stack of a plurality of optical element array units eachhaving an optical element and a substrate, the substrate having one ormore grooves each suited to a profile of said optical element on one ofsurfaces thereof, and one or more optical elements being aligned andfixed in the grooves, characterized in that said plurality of opticalelement array units are stacked in a state that surfaces facing eachother of the substrates among adjacent two units out of said pluralityof optical element array units are not contacted directly each other,and that said adjacent two units do not give a direct mechanicalinfluence each other.
 2. The two-dimensional optical element arrayaccording to claim 1, wherein said optical element is an optical fiberor lens.
 3. The two-dimensional optical element array according to claim1, wherein an apex of an optical element arranged on the substrate ofone of said optical element array units is brought into contact with asurface, facing thereto, of the substrate of another of said opticalelement array units, and surfaces facing each other of the substrates ofadjacent two of said plurality of optical element array units are keptfrom direct contact with each other, and that said adjacent two units donot give a direct mechanical influence each other.
 4. Thetwo-dimensional optical element array according to claim 1, wherein saidplurality of optical element array units are stacked in a state that anadhesive layer is interposed between an apex of an optical elementarranged on the substrate of one of said optical element array units anda surface, facing thereto, of the substrate of another of said opticalelement array units, said apex of the optical element and said surfaceof the substrate are brought into contact with said adhesive layer, andthe surfaces facing each other of the substrates of adjacent two of saidoptical element array units are not contacted directly each other, andthat said adjacent two units do not give a direct mechanical influenceeach other.
 5. The two-dimensional optical element array according toclaim 1, further comprising a fixing member on one of surfaces of saidsubstrate of the uppermost optical element array unit and between saidsubstrates of adjacent optical element array units, the fixing memberpressing or mounting said optical element against or on one surface withsaid grooves of said substrate for alignment and fixing.
 6. Thetwo-dimensional optical element array according to claim 5, wherein saidfixing member presses or mounts said optical element against or onto thesurface with said grooves of said substrate for alignment and fixing insuch a manner that a surface of said fixing member and a surface of saidsubstrate of said optical element array unit which faces to the surfaceof the fixing member are not contacted directly each other, and thatsaid adjacent two units do not give a direct mechanical influence eachother.
 7. The two-dimensional optical element array according to claim5, wherein said optical element is pressed against or mounted on saidsubstrate for alignment and fixing in such a manner that said opticalelement abuts on a surface of said fixing member and on a side wall ofsaid groove.
 8. The two-dimensional optical element array according toclaim 5, further comprising an adhesive layer between the surface ofsaid fixing member and the surface of said substrate of said opticalelement array unit which faces to the surface of the fixing member. 9.The two-dimensional optical element array according to claim 8, whereina thickness of said adhesive layer falls within a range from 2 to 100μm.
 10. The two-dimensional optical element array according to claim 1,wherein a positioning guide is formed at a predetermined position in thesurface with said grooves of said substrate of said optical elementarray unit.
 11. The two-dimensional optical element array according toclaim 1, wherein said groove is a V-shaped groove.
 12. Thetwo-dimensional optical element array according to claim 1, wherein alight-emitting end face and/or light receiving end face of said opticalelement of said optical element array unit is provided by slanting it(or them) a predetermined angle (θ) with respect to a planeperpendicular to a central axis of the optical element.
 13. Thetwo-dimensional optical element array according to claim 12, wherein thelight-emitting end face and/or light receiving end face of said opticalelement is disposed in said plane perpendicular to the central axis ofthe optical element.
 14. The two-dimensional optical element arrayaccording to claim 12, wherein the light-emitting end face and/or lightreceiving end face of said optical element is disposed in a plane angledby a predetermined angle (θ) with respect to said plane perpendicular tothe central axis of the optical element.
 15. The two-dimensional opticalelement array according to claim 12, wherein the light-emitting end faceand/or light receiving end face of said optical element is disposed in aplane perpendicular to an optical axis of an emitted light and/orincident light, respectively.
 16. A method of measuring a core positionof an optical element of a two-dimensional optical element array whichcomprises a stack of a plurality of optical element array units eachhaving an optical element and a substrate, the substrate having one ormore grooves each suited to a profile of said optical element on one ofsurfaces thereof, and one or more optical elements being aligned andfixed in the grooves, wherein said plurality of waveguide substrateunits are stacked in a state that surfaces facing each other of thesubstrates among adjacent two units out of said plurality of opticalelement array units are not contacted directly each other, and that saidadjacent two units do not give a direct mechanical influence each other,characterized in that the said method comprises the steps of: measuringcore positions of m rows of optical elements and measuring corepositions of at least two of n columns of optical elements in the casewhere m optical element array units are stacked and each optical elementarray unit has n channels (in the case where said optical elements arearranged in m rows and n columns); designating arbitrarily one opticalelement for each of said at least two columns of optical elements andmeasuring a distance D between the core positions of said opticalelements designated (designated optical elements); and calculating apositional relation among elements of a matrix of the core positions ofsaid optical elements at four corners of a rectangular having a linesegment connecting the core positions of said designated opticalelements as a diagonal line thereof and calculating the core positionsof all of said optical elements.
 17. A two-dimensional waveguideapparatus, comprising a stack of a plurality of waveguide substrateunits each having one or more waveguides patterned in a planar manner,characterized in that said plurality of waveguide substrate units arestacked in a state that surfaces facing each other of the substratesamong adjacent two units out of said plurality of optical element arrayunits are not contacted directly each other, and that said adjacent twounits do not give a direct mechanical influence each other.
 18. Thetwo-dimensional waveguide apparatus according to claim 17, furthercomprising an adhesive layer between the surfaces facing each other oftwo adjacent waveguide substrate units of said plurality of waveguidesubstrate units.
 19. The two-dimensional waveguide apparatus accordingto claim 17, wherein a thickness of said adhesive layer falls within arange from 2 to 100 μm.
 20. The two-dimensional waveguide apparatusaccording to claim 17, wherein a positioning guide is formed at apredetermined location on a surface of said waveguide substrate unit.21. The two-dimensional waveguide apparatus according to claim 17,wherein a light-emitting end face of each waveguide said waveguidesubstrate unit is slanted by a predetermined angle (θ) with respect to aplane perpendicular to an optical axis thereof.
 22. The two-dimensionalwaveguide apparatus according to claim 21, wherein the light-emittingend face and/or light receiving end face of said waveguide of saidwaveguide substrate unit is disposed in a plane perpendicular to acentral axis of said waveguide.
 23. The two-dimensional waveguideapparatus according to claim 21, wherein the light-emitting end faceand/or light receiving end face of said waveguide of said waveguidesubstrate unit is disposed in a plane angled by a predetermined angle(θ) with respect to said plane perpendicular to the central axis of saidwaveguide.
 24. The two-dimensional waveguide apparatus according toclaim 21, wherein the light-emitting end face and/or light receiving endface of said waveguide of said waveguide substrate unit is disposed in aplane perpendicular to an optical axis of an emitted light and/orincident light, respectively.